This invention is directed generally to electrical devices and, more specifically, to a latching feature used in a current tripping mechanism for a circuit breaker.
Electrical devices, such as circuit breakers, are widely used in diverse residential, commercial, and industrial electric systems, being indispensable components of such systems in protecting against over-current conditions. In response to application-specific needs, such as space constraints, efficiency, capacity, response time, and type of reset function (manual or remote), a multitude of different circuit breakers have been developed.
One type of circuit breaker that has been developed uses a thermo-magnetic tripping device to trip a latch in response to a specific range of over-current conditions. One feature of this type of circuit breaker is an electromagnet arrangement that includes a yoke and an armature. In the presence of a very high current, or short circuit condition, the yoke and armature are attracted to each other to release the latch and cause a tripping condition, which results in the interruption of current flow through the electrical system associated with the circuit breaker. Another feature of this type of circuit breaker is a bimetal arrangement that comprises a bimetal element and a trip lever. A function of the bimetal arrangement is to trip the circuit breaker by causing a significant deflection in the bimetal element, which responds to changes in temperature due to resistance heating caused by the flow of the circuit""s electric current through the bimetal. Typically, the bimetal element is in the form of a blade and it operates together with a latch. Heating the bimetal to a predetermined level causes it to deflect and to release the trip lever from the latch after a time delay that corresponds to a predetermined over-current threshold. Consequently, the current circuit that is associated with the bimetal is broken.
The latch is generally a flat piece of metal, such as a stainless steel plate, that is installed on the armature and that functions to hold the trip lever in the tripped position until a predetermined condition occurs, such as the manual resetting of the circuit breaker. The latch is usually hardened to provide a wear resistant surface, and is typically greased to reduce friction between the trip lever and the latch. During the normal operation of the circuit breaker debris is created that is caught in the grease on the latch surface. The movement of the trip lever between a latched and a tripped position can pull the debris along the surface of the latch plate and damage the surface of the latch. An undesired effect of a damaged latch surface is that a higher than normal unlatching force may be required. Therefore, to avoid damage the latch surface requires frequent cleaning. Another undesired effect of a damaged latch surface is that the circuit breaker may possibly malfunction, wherein debris lodged between the latch and the trip lever could prevent any further movement of the trip lever and make the circuit breaker inoperable.
Accordingly, there is a need for an improved circuit breaker that avoids the above mentioned problems.
Briefly, in accordance with the foregoing, the invention relates to an electrical device, such as a circuit breaker, for interrupting the flow of current, which comprises a housing, a stationary contact, a blade having a movable contact, a releasably latchable trip lever, a bimetal, and a magnetic armature. The movable contact is movable into and out of engagement with the stationary contact, and the trip lever, which is pivotally mounted in the housing, is releasable from a latched position for movement to a tripped position to cause separation of the stationary and movable contacts. The bimetal causes the release of the trip lever from the latched position by having the magnetic armature, which is pivotally connected to the bimetal, drawn a predetermined distance in response to a predetermined short circuit current flowing through the bimetal. The trip lever is held in the latched positioned by a latch which is positioned near an opening located in the magnetic armature. The latch is made of a hardened, relative to the armature, material and it has a minimal surface area. When the predetermined short circuit current flows through the bimetal, the trip lever moves to the tripped position.